Search found 59 matches

by lukezhang2C
Sun Mar 17, 2019 4:44 pm
Forum: Second Order Reactions
Topic: Non-integer orders
Replies: 3
Views: 181

Re: Non-integer orders

The only non-integer order which is mentioned in the book which occurs commonly would be the 1/2 order, but the rest should be ranging from 0-3 at most.
by lukezhang2C
Sun Mar 17, 2019 4:43 pm
Forum: Second Order Reactions
Topic: Half Life
Replies: 5
Views: 452

Re: Half Life

Half life equations are given in the equation sheet, but they will not tell you which half-life equation corresponds to which order of reaction. You can also derive them using the standard half life equation, solving for t when the concentrations are half of the initial.
by lukezhang2C
Sun Mar 17, 2019 4:41 pm
Forum: Zero Order Reactions
Topic: Reaction Rate
Replies: 10
Views: 281

Re: Reaction Rate

when given a table, you can use any reaction and the values to kind K, right? Yes, you should be able to use any of the values given to find k as long as they correspond to one another. For example, using random concentrations for an initial rate which was found using other concentrations would not...
by lukezhang2C
Sun Mar 17, 2019 4:35 pm
Forum: Zero Order Reactions
Topic: Reaction Rate
Replies: 10
Views: 281

Re: Reaction Rate

What is a reaction rate and how does it relate to the rate law? The reaction rate is the rate of which the reaction proceeds (in M/s) and is related to the rate law as the rate law is used to calculate the initial rates of the reaction. In a problem typically we would use the reaction rate to find ...
by lukezhang2C
Sun Mar 17, 2019 4:34 pm
Forum: Zero Order Reactions
Topic: Reaction Rate
Replies: 10
Views: 281

Re: Reaction Rate

Yes, the K value should be the same for all since you need to use the different concentrations and initial rates in order to find K in the first place.
by lukezhang2C
Sun Mar 17, 2019 4:33 pm
Forum: Zero Order Reactions
Topic: Zero Order Reaction Example
Replies: 2
Views: 163

Re: Zero Order Reaction Example

A zero order reaction is one where changing the concentration of your reactants does not change the initial rate of the reaction, meaning that your reaction rate is independant of that reactant. Zero order reaction K values will have M/s units.
by lukezhang2C
Sun Mar 17, 2019 4:30 pm
Forum: Zero Order Reactions
Topic: Zero order reaction
Replies: 8
Views: 235

Re: Zero order reaction

You can determine experimentally, when observing that the initial rates don't change when changing the concentration of the reactants, or by looking at your K units as your K would have to be in the units of M/s to offset the unitless reactant.
by lukezhang2C
Sun Mar 17, 2019 4:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equlibrium and catalysts
Replies: 2
Views: 167

Re: Equlibrium and catalysts

Catalysts lower the activation energy needed for a reaction to proceed, but should not innately change anything about the equilibrium. It would only serve to shift the reaction to the right as more products would be made.
by lukezhang2C
Sun Mar 17, 2019 3:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K and Kc
Replies: 6
Views: 245

Re: K and Kc

K and Kc can mean similar things depending on the context of the problem, but Kp would mean partial pressures while Kc would mean concentration.
by lukezhang2C
Sun Mar 17, 2019 3:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka Kb = Kw
Replies: 5
Views: 259

Re: Ka Kb = Kw

Kw is typically used to find Ka or Kb when given the other. The relation can be used in any number of ways depending on the problem and what you need to find.
by lukezhang2C
Sun Mar 17, 2019 3:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka vs. Kb
Replies: 12
Views: 346

Re: Ka vs. Kb

Ka is the ionisation constant, used when dealing with acids and excess protons in a solution. Kb is typically used with bases, and finding the pOH of a solution. Kc is just the relation of Ka and Kb which is Ka X Kb = 10^-14
by lukezhang2C
Sun Mar 17, 2019 3:33 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: atm to torr
Replies: 3
Views: 203

Re: atm to torr

1 ATM = 760 torr and it is always on the equation sheet! Just remember to use the correct constants after converting from atm to torr!
by lukezhang2C
Sun Mar 17, 2019 3:28 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Deriving Enthalpy Equations
Replies: 3
Views: 217

Re: Deriving Enthalpy Equations

For any derivations which I've had to do I always start by finding common factors/variables and playing around with them with substitution until I get the equation whic I need. Always look at which variables need to cancel and which ones you would need to keep, it is a crucial factor in derivations.
by lukezhang2C
Sun Mar 17, 2019 3:25 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: [tex]\Delta U = \Delta H[/tex]
Replies: 2
Views: 230

Re: [tex]\Delta U = \Delta H[/tex]

So delta U = delta H is only considered a very specific case of the original equation, which is delta U = q + w = q - P delta V. You can only use delta U = delta H when q = delta H and you are under constant pressure, otherwise you cannot use the other equation.
by lukezhang2C
Sun Mar 17, 2019 3:22 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: delta H of reaction
Replies: 2
Views: 227

Re: delta H of reaction

Enthalpy is a property which varies with the moles of reactants/products present, and oftentimes the units would be KJ/mole or would ask you to find it permole, so it makes sense to make stoichiometrically correct calculations when finding the enthalpy of the reaction.
by lukezhang2C
Sun Mar 17, 2019 3:19 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Cp vs Cv
Replies: 6
Views: 495

Re: Cp vs Cv

Cp represents constant pressure while Cv represents constant volume, our problems will tell us whether or not we would be dealing with constant pressure or volume as one with two changing conditions would be extremely difficult, and would have to use another approach entirely.
by lukezhang2C
Sun Mar 17, 2019 3:17 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Midterm Question 6
Replies: 6
Views: 263

Re: Midterm Question 6

I think for this question on the midterm it was far easier to approach it by finding the net moles of gas produced than it was to calculate each bond enthalpy as you have delta U = delta H (which is found by multiplying the delta H given by 4 moles) - nRT where your n is just the net change in moles...
by lukezhang2C
Sun Mar 17, 2019 3:13 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: q and delta H
Replies: 6
Views: 265

Re: q and delta H

So Delta U = q + w = q - PdeltaV, meaning that under constant pressure U = q = delta H. This is where most of the interchangeability comes from as systems with constant pressure appear often in our problems.
by lukezhang2C
Sun Mar 17, 2019 3:11 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: When is delta U = 0?
Replies: 4
Views: 222

Re: When is delta U = 0?

Looking at the equation Delta U = q + w, delta U is only 0 when q = -w which means heat put into the system is equal to the heat out of the system, in other words the system is isolated with no net change in internal energy.
by lukezhang2C
Sun Mar 17, 2019 3:08 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Drawing cells
Replies: 3
Views: 210

Re: Drawing cells

A general cell diagram would be something like this for a Galvanic cell:

Conducting Solid | Anode || Cathode | Conducting Solid

Different states of matter are separated by | while different species of the same state are separated by commas
by lukezhang2C
Sun Mar 17, 2019 3:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test #2: Question #4, Parts A and B
Replies: 2
Views: 175

Re: Test #2: Question #4, Parts A and B

The balanced overall cell reaction that I got was 2N02 + 2H20 + Zn2+ --> Zn (S) + NO3- + 4H+, and I also got the cell diagram wrong. However from what I can ascertain you needed to flip No3 and Zn, and include a solid for the NO3 side.
by lukezhang2C
Sun Mar 17, 2019 3:01 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: E cell
Replies: 3
Views: 195

Re: E cell

It's not usually negative in the way that time can't be negative in a physics problem, but for the sake of some calculations we can set it to be negative. When flipping the equation for a half reaction your E can be negative at times, which may contribute to this as well.
by lukezhang2C
Sun Mar 17, 2019 2:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram and Ecell [ENDORSED]
Replies: 8
Views: 27302

Re: Cell Diagram and Ecell [ENDORSED]

For a Galvanic Cell it should be Anode || Cathode, where there are single lines (|) separating different states of matter, and commas separating different agents with the same state of matter. i.e (aq), (aq), || (aq)| (s)
by lukezhang2C
Sun Mar 17, 2019 2:56 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Reducing Power
Replies: 3
Views: 215

Re: Reducing Power

It is due to the fact that a stronger reduction power indicates higher electronegativity, which makes for a stronger oxidising agent. Stronger reduction power also corresponds with a higher E value, which also increases oxidising power.
by lukezhang2C
Tue Feb 12, 2019 10:21 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Equations
Replies: 5
Views: 267

Equations

Which equations would be good to memorise for the midterm?
by lukezhang2C
Tue Feb 12, 2019 10:20 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Midterm #1 14B
Replies: 17
Views: 552

Re: Midterm #1 14B

I don't see any other worksheets posted :(
by lukezhang2C
Fri Jan 18, 2019 11:03 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka vs. Kb
Replies: 12
Views: 346

Re: Ka vs. Kb

Ka and Kb are just used for acid/base dissociation, and Kc is just the equilibrium concentration.
by lukezhang2C
Fri Jan 18, 2019 11:00 am
Forum: Ideal Gases
Topic: Chemistry Community Posting
Replies: 7
Views: 155

Chemistry Community Posting

Should we finish our three posts before our discussion date or before/on Friday?
by lukezhang2C
Fri Jan 18, 2019 10:59 am
Forum: Ideal Gases
Topic: Homework Week 2
Replies: 10
Views: 185

Re: Homework Week 2

Homework will now be due in discussion!
by lukezhang2C
Sat Dec 08, 2018 12:06 am
Forum: Ionic & Covalent Bonds
Topic: Test bank?
Replies: 9
Views: 423

Re: Test bank?

Anyone have any past final exam questions from Lavelle from the test bank?
by lukezhang2C
Sat Dec 08, 2018 12:00 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: strong vs weak acids
Replies: 5
Views: 116

Re: strong vs weak acids

Electronegativity is also a factor to consider!
by lukezhang2C
Fri Dec 07, 2018 11:59 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Oxygen atoms in acid structures?
Replies: 3
Views: 275

Re: Oxygen atoms in acid structures?

I'm guessing it's because this would make the molecule larger while also making it more electronegative, which makes it a stronger acid, but I'm not 100% sure.
by lukezhang2C
Fri Dec 07, 2018 11:56 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Factors for Acid Stength [ENDORSED]
Replies: 3
Views: 134

Re: Factors for Acid Stength [ENDORSED]

The more electronegative the atom is the stronger the acid due to the strong ionic nature of their electron-sharing nature!
by lukezhang2C
Fri Nov 30, 2018 1:57 pm
Forum: Administrative Questions and Class Announcements
Topic: How to find my posts
Replies: 45
Views: 36919

Re: How to find my posts

I believer you can have email notifications, but I'm not sure how practical that would be.
by lukezhang2C
Fri Nov 30, 2018 10:59 am
Forum: Air Pollution & Acid Rain
Topic: Acid Rain on the Final
Replies: 4
Views: 260

Acid Rain on the Final

Will we have to memorise the exact chemical reaction equation for acid rain?
by lukezhang2C
Fri Nov 30, 2018 10:39 am
Forum: Air Pollution & Acid Rain
Topic: Acid Rain
Replies: 9
Views: 963

Re: Acid Rain

The water molecules in rain react with pollutants in the air and becomes acidic in nature
by lukezhang2C
Fri Nov 30, 2018 10:38 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH formula
Replies: 5
Views: 279

Re: pH formula

They might give us a new equation sheet but I'm pretty sure you're just supposed to memorise it.
by lukezhang2C
Fri Nov 30, 2018 10:37 am
Forum: Formal Charge and Oxidation Numbers
Topic: TEST 3
Replies: 4
Views: 315

Re: TEST 3

I would not think so, though it's a relatively simple formula so they might expect you to memorise it.
by lukezhang2C
Fri Nov 30, 2018 10:36 am
Forum: Sigma & Pi Bonds
Topic: Sigma and Pi bonds
Replies: 5
Views: 150

Re: Sigma and Pi bonds

Most likely nothing computational as we don't know enough to do that, I would assume just labeling would work
by lukezhang2C
Fri Nov 30, 2018 10:35 am
Forum: Calculating the pH of Salt Solutions
Topic: Ka Constant
Replies: 4
Views: 241

Ka Constant

Do we need to know how to calculate the Ka equilibrium of acid/base reactions?
by lukezhang2C
Sat Nov 17, 2018 1:56 am
Forum: Sigma & Pi Bonds
Topic: Sigma v. Pi
Replies: 6
Views: 216

Re: Sigma v. Pi

Sigma bonds result from overlapping end-end atomic orbitals while pi bonds are overlapping side to side in a perpendicular plane.
by lukezhang2C
Sat Nov 17, 2018 1:53 am
Forum: Hybridization
Topic: Test 3
Replies: 5
Views: 156

Re: Test 3

His outline would give all necessary information, and he would probably email us as well soon!
by lukezhang2C
Sun Nov 04, 2018 9:58 pm
Forum: Electronegativity
Topic: Periodic Trends
Replies: 10
Views: 292

Re: Periodic Trends

For Atomic Radius it increases as it goes down due to the added number of shells to house the electrons
by lukezhang2C
Sun Nov 04, 2018 9:57 pm
Forum: Electronegativity
Topic: MIDTERM
Replies: 5
Views: 130

Re: MIDTERM

Will we be given the electronegativity difference numbers for non-obvious cases of covalent or ionic bonding?
by lukezhang2C
Sun Nov 04, 2018 9:56 pm
Forum: Ionic & Covalent Bonds
Topic: Test bank?
Replies: 9
Views: 423

Re: Test bank?

The Bruin Online Testbank has previous chem 14A exams too but not from Lavelle
by lukezhang2C
Thu Oct 25, 2018 11:18 pm
Forum: Photoelectric Effect
Topic: Conditions that allow electron to be ejected from metal surface
Replies: 12
Views: 444

Re: Conditions that allow electron to be ejected from metal surface

Will the work function of the metal be given when doing problems?
by lukezhang2C
Thu Oct 25, 2018 11:15 pm
Forum: Properties of Light
Topic: Test 2
Replies: 7
Views: 263

Re: Test 2

Which equations do we have to memorise vs which ones are on the equation sheet?
by lukezhang2C
Thu Oct 25, 2018 11:14 pm
Forum: Einstein Equation
Topic: Units
Replies: 17
Views: 580

Re: Units

It should follow e=mc^2 for photons, which is kgm^2/s^2
by lukezhang2C
Thu Oct 18, 2018 7:57 pm
Forum: Properties of Electrons
Topic: Diffraction patterns
Replies: 9
Views: 200

Re: Diffraction patterns

Constructive interference simply means that an addition of the two waves results in a larger amplitude, while destructive interference is the opposite. The two are not mutually exclusive and can be in conjunction with one another.
by lukezhang2C
Thu Oct 18, 2018 7:55 pm
Forum: Properties of Electrons
Topic: Energy v. Kinetic Energy
Replies: 3
Views: 96

Re: Energy v. Kinetic Energy

Electrons have different properties than photons, and while it is near massless, it is often not considered as such when solving for kinetic energy which is why the same kinetic energy equations which work for photons do not work for electrons.
by lukezhang2C
Thu Oct 18, 2018 7:53 pm
Forum: Properties of Light
Topic: Wavelength and frequency proportions [ENDORSED]
Replies: 5
Views: 167

Re: Wavelength and frequency proportions [ENDORSED]

The two have an inversely proportional relationship, this property is just derived from the formula!
by lukezhang2C
Fri Oct 12, 2018 12:12 am
Forum: Administrative Questions and Class Announcements
Topic: Number of questions on test one [ENDORSED]
Replies: 39
Views: 17750

Re: Number of questions on test one [ENDORSED]

Does anyone know if there will be a periodic table provided for us?
by lukezhang2C
Fri Oct 12, 2018 12:10 am
Forum: SI Units, Unit Conversions
Topic: formula units [ENDORSED]
Replies: 69
Views: 22615

Re: [ENDORSED]

Simran Athwal-Dis 3A wrote:Hi, I had a quick question. How do we check how many times we posted on Chemistry Community? Do we go on our profile?


I think theres an option in profile which shows your posts!
by lukezhang2C
Fri Oct 12, 2018 12:08 am
Forum: Administrative Questions and Class Announcements
Topic: Number of questions on test one [ENDORSED]
Replies: 39
Views: 17750

Re: Number of questions on test one [ENDORSED]

Diana Chavez 1K wrote:If we do not understand what a question on the test asks is it allowed to ask for clarity from our TA's?

I think in general during testing they're not really allowed to answer these types of questions unless it's a glaring wording error.
by lukezhang2C
Mon Oct 01, 2018 1:57 pm
Forum: Significant Figures
Topic: Significant Figures [ENDORSED]
Replies: 6
Views: 157

Re: Significant Figures [ENDORSED]

Significant figures allows us to measure the precision of our measurement instruments!
by lukezhang2C
Mon Oct 01, 2018 1:54 pm
Forum: SI Units, Unit Conversions
Topic: Week 1 Homework Assignment [ENDORSED]
Replies: 16
Views: 461

Re: Week 1 Homework Assignment [ENDORSED]

Yep! You do any seven problems from the assigned problems and turn it in.
by lukezhang2C
Mon Oct 01, 2018 2:58 am
Forum: SI Units, Unit Conversions
Topic: Homework Grading Clarification [ENDORSED]
Replies: 8
Views: 301

Homework Grading Clarification [ENDORSED]

So for the homework we turn in, do we pick seven problems from the list on the syllabus or should we turn in our answers to all of the problems but the TAs would only grade seven of them?

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